Your small intestine does most of the digesting of the foods you eat. If you have a malabsorption syndrome, your small intestine cannot absorb nutrients from foods. Causes of malabsorption syndromes include. 1  Celiac disease. 2  Lactose intolerance.  Short bowel syndrome. This happens after surgery to remove half or more of the small intestine. You might need the surgery if you have a problem with the small intestine from a disease, injury, or birth defect.
The exhaust manifold obviously carries exhaust away from the engine compartment. When the manifold fails to completely perform that function, fumes can enter the coach. This was not detected however in my coach so that telltale signal was missing. The manifold if leaking can reportedly injure the engine. And exhaust gases are used by the turbo system. If that is not performed well, you will notice a loss of boost (power) and mpg. If left unattended (repaired) the leak can also leak hot gasses into equipment and areas where it does not belong.
Imo, what must be done is break the bond between the bolt and the head. Heating the head will expand the iron and allow the oil or wax to get in to the threads. Torching or cutting the heads off of the bolts to get the manifold off first will help. You can weld a 7/16 or 1/2 hex nut back on to make the job easier.